fix: add compatibility for Zig 0.16 ArrayList and timer changes

[jinzhongjia]

• Replace legacy ArrayList initializers with initCapacity() in relevant places to support Zig 0.16, preserving compatibility with older releases.
• Update benchmarks to use platform time routines when std.time.Timer is removed in Zig 0.16, and switch to page_allocator where GeneralPurposeAllocator is no longer available.
• Expand workflow support to include Zig 0.16.0.
• Clarify version support and adaptation details in documentation.

[gemini-code-assist]

Code Review

This pull request introduces support for Zig 0.16.0, updating version compatibility documentation and adapting the codebase to API changes in ArrayList initialization, timing, and memory allocation. Feedback focuses on correcting the false claim that GeneralPurposeAllocator was removed, suggesting the use of std.time.Instant for cross-platform timing, and recommending more idiomatic ArrayList initialization for Zig 0.16. Additionally, the reviewer advises against using page_allocator in benchmarks to avoid performance regressions.

[gemini-code-assist]

The claim that std.heap.GeneralPurposeAllocator is removed in Zig 0.16 is incorrect. It remains a core part of the standard library, although its internal implementation details or its location within std.heap may have evolved. Switching to page_allocator in benchmarks is a regression in measurement quality as it is significantly slower due to per-allocation system calls.

[gemini-code-assist]

The manual implementation of getTimeNs introduces significant boilerplate and potential portability issues (e.g., dependency on libc for clock_gettime on non-Windows platforms). For Zig 0.16, the recommended replacement for std.time.Timer is std.time.Instant, which provides a cross-platform monotonic clock API. Additionally, the Windows implementation lacks a check for a zero frequency from RtlQueryPerformanceFrequency, which would cause a division by zero.

[gemini-code-assist]

The else if (builtin.os.tag != .windows) condition is redundant following the initial if (builtin.os.tag == .windows). This makes the final else block containing the @compileError unreachable. It should be simplified to a standard else block.

    } else {
        var ts: std.c.timespec = undefined;
        _ = std.c.clock_gettime(std.c.CLOCK.MONOTONIC, &ts);
        return @as(u64, @intCast(ts.tv_sec)) * std.time.ns_per_s + @as(u64, @intCast(ts.tv_nsec));
    }

[gemini-code-assist]

Using std.heap.page_allocator for benchmarks is generally discouraged because it performs a system call for every allocation and deallocation, which can dominate the benchmark results and hide the actual performance characteristics of the code being tested. Since GeneralPurposeAllocator is still available in Zig 0.16, it should be used instead.

[gemini-code-assist]

The conditional logic for handling the timer across Zig versions is quite clunky. Instead of manually implementing getTimeNs and using a void type for legacy_timer, it is recommended to use std.time.Instant for Zig 0.16. This would allow for a cleaner abstraction or a simple wrapper that works across all supported versions.

[gemini-code-assist]

Using initCapacity(alloc, 0) catch unreachable is suboptimal and introduces a potential crash point during memory cleanup. In Zig 0.16, std.ArrayList(T).init(allocator) is the preferred way to initialize a managed ArrayList as it does not perform an initial allocation and thus cannot fail. The logic can be simplified to use init for both 0.14 and 0.16, only using the struct literal for 0.15 where the ArrayList was unmanaged.

                    var new_heap = if (current_zig.minor == 15)
                        std.ArrayList(Payload){}
                    else
                        std.ArrayList(Payload).init(alloc);

[gemini-code-assist]

Similar to the previous comment, std.ArrayList(T).init(allocator) should be used for Zig 0.14 and 0.16 to avoid the unnecessary try or catch unreachable on an operation that doesn't need to allocate memory initially.

            var parse_stack = if (current_zig.minor == 15)
                std.ArrayList(ParseState){}
            else
                std.ArrayList(ParseState).init(allocator);

[gemini-code-assist]

The use of initCapacity(allocator, 0) catch unreachable throughout the test suite is repetitive and less idiomatic than using init(allocator) for versions where the ArrayList is managed (0.14 and 0.16).

    var input = if (builtin.zig_version.minor == 15)
        std.ArrayList(u8){}
    else
        std.ArrayList(u8).init(allocator);